Electronic documents of various sorts are ubiquitous in modern business. These documents include text-based documents produced using word processing software, presentations, graphical images, audio recordings, and video clips. It is frequently advantageous to mark-up or annotate such documents to indicate changes, ask questions, make comments, or note particularly important sections of the documents. Such annotation is frequently made by adding handwritten marks to a printed copy of a document. Text documents are also frequently annotated in word processing software, where the changes or comments are tracked within the text document itself. Such annotations within text documents are limited to structured text or the addition of certain types of graphical images. With the recent advent of touchscreens in devices such as tablet computers and smartphones, electronic annotation has significantly improved to allow free-form commenting by hand. Such annotation is greatly preferred by many users because it offers flexibility to annotate by, for example, circling sections, drawing arrows, or drawing schematic diagrams.
Some existing tools for annotation of electronic documents exist that allow users to add handwritten or other marks to some types of electronic documents. For example, the iAnnotate® software application by Branchfire, Inc., receives and stores user comments as part of certain page-based documents. The annotations become part of the annotated document, however, and cannot be sent to another user without sending the full document. Such approach is implemented in the widely used Portable Document Format (PDF) file format to store annotations within each PDF file, regardless of whether such PDF files are processed by Adobe Acrobat® or various other programs (e.g., Preview by Apple Inc.). This can lead to problems when multiple users simultaneously annotate copies of the same document, because neither annotated document will have the full set of annotations. All programs using the built-in annotation capabilities of PDF files inherently suffer from the problems associated with storing the annotations as part of the file, as do other built-in annotations (such as the annotation functions in Microsoft Word®). Attempts to allow simultaneous annotation have focused on version management approaches that attempt to frequently synchronize the document versions of the users or attempt to merge multiple copies of the document. Each of these approaches significantly increases processor usage, data transmission between users (which requires greater network bandwidth), and complexity of the annotation software. Additionally, current approaches hinder the ability to convert documents between different formats without losing the annotations. The invention described herein is addressed to improving software tools for annotation of electronic documents.